Polypropylene is generally produced using either a metallocene or a Ziegler-Natta (ZN) catalyst system.
Plastics used in certain laboratory and medical equipment must have low fluid retention and other necessary qualities, including clarity, flexibility, radiation resistance, and autoclavability.
Ziegler-Natta produced polypropylene (ZN-PP) can be prone to warpage in the produced articles, due to its having a wider molecular weight distribution than metallocene produced polypropylene (mPP). In a process known in the art to produce the ZN polypropylene with a narrow molecular weight distribution, the polymers are “vis-broken” in a controlled rheological manner by introducing a specific concentration of a peroxide chemical during extrusion. This controlled rheology polypropylene (CR-PP) can lack some of the performance characteristics of metallocene produced polypropylene, particularly fluid retention. Specifically, additive formulations used in mPP polymers do not achieve the same low fluid retention properties when used in CR-PP.